Biology Vocabulary (G-2)

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Aminoacyl-tRNA Synthetase

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Any of a group of enzymes that attach specific amino acids to the correct tRNA during the tRNA-charging reaction. Each of the 20 amino acids has a corresponding enzyme.

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Amniocentesis

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Indirect examination of a fetus by tests on cultures grown from fetal cells obtained from a sample of the amniotic fluid or tests on the fluid itself.

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Amnion

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The innermost of the extraembryonic membranes; the amnion forms a fluid-filled sac around the embryo in amniotic eggs.

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Amniote

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A vertebrate that produces an egg surrounded by four membranes, one of which is the amnion; amniote groups are the reptiles, birds, and mammals.

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Amniotic egg

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An egg that is isolated and protected from the environment by a more or less impervious shell during the period of its development and that is completely self-sufficient, requiring only oxygen.

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Ampulla

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In echinoderms, a muscular sac at the base of a tube foot contracts to extend the tube foot.

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Amyloplast

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A plant organelle called a plastid that specializes in storing starch.

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Anabolism

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The biosynthetic or constructive part of metabolism; those chemical reactions involved in biosynthesis.

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Anaerobic

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Any process that can occur without oxygen, such as anaerobic fermentation or H2S photosynthesis.

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Anaerobic respiration

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The use of electron transport to generate a proton gradient for chemiosmotic synthesis of ATP using a final electron acceptor other than oxygen.

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Analogous

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Structures that are similar in function but different in evolutionary origin, such as the wing of a bat and the wing of a butterfly.

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Anaphase

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In mitosis and meiosis 2, the stage initiated by the separation of sister chromatids, during which the daughter chromosomes move to opposite poles of the cell; in meiosis 1, marked by separation of replicated homologous chromosomes.

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Anaphase-promoting complex (APC)

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A protein complex that triggers anaphase; it initiates a series of reactions that ultimately degrades cohesin, the protein complex that holds the sister chromatids together. The sister chromatids are them released and move toward opposite poles in the cell.

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Anchoring junction

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A type of cell junction that mechanically attaches the cytoskeleton of a cell to the cytoskeletons of adjacent cells or to the extracellular matrix.

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Androecium

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The floral whorl that comprises the stamens.

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Aneuploidy

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The condition in an organism whose cells have lost or gained a chromosome; down syndrome, which results from an extra copy of human chromosome 21, is an example of aneuploidy in humans.

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Angiosperms

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The flowering plants, one of five phyla of seed plants. In angiosperms, the ovules at the time of pollination are completely enclosed by tissues.

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Animal pole

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In fish and other aquatic vertebrates with asymmetrical yolk distribution in their eggs, the hemisphere of the blastula comprising cells relatively poor in yolk.

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Anion

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A negatively charged ion.

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Annotation

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In genomics, the process of identifying and making note of "landmarks" in a DNA sequence to assist with recognition of coding and transcribed regions.

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Anonymous markers

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Genetic markers in a genome that do not cause a detectable phenotype, but that can be detected using molecular techniques.

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Antenna complex

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A complex of hundreds of pigment molecules in a photosystem that collects photons and feeds the light energy to a reaction center.

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Anther

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In angiosperm flowers, the pollen-bearing portion of a stamen.

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Antheridium, plural: antheridia

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A sperm producing organ.

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Anthropoid

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Any member of the mammalian group consisting of monkeys, apes, and humans.

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Antibody

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A protein called immunoglobulin that is produced by lymphocytes in response to a foreign substance (antigen) and released into the bloodstream.

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Anticodon

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The three-nucleotide sequence at the end of a transfer RNA molecule that is complimentary to, and base-pairs with, an amino-acid-specifying codon in messenger RNA.

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Antigen

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A foreign substance, usually a protein or polysaccharide, that stimulates an immune response.

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Antiporter

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A carrier protein in a cell's membrane that transports two molecules in opposite directions across the membrane.

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Anus

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The terminal opening of the gut; the solid residues of digestion are eliminated through the anus.

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Aorta

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The major artery of vertebrate systemic blood circulation; in mammals, Carrie's oxygenated blood away from the heart to all regions of the body except the lungs.

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Apical meristem

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In vascular plants, the growing point at the tip of the root or stem.

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Apoplast route

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In plant roots, the pathway for movement of water and minerals that leads through cell walls and between cells.

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Apoptosis

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A process of programmed cell death, in which dying cells shrivel and shrink; used in all animal cell development to produce planned and orderly elimination of cells not destined to be present in the final tissue.

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Aposematic coloration

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An ecological strategy of some organisms that "advertise" their poisonous nature by the use of bright colors.

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Aquaporin

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A membrane channel that allows water to cross the membrane more easily than by diffusion through the membrane.

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Aquifers

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Permeable, saturated, underground layers of rock; sand, and gravel, which serve as reservoirs for groundwater.

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Archegonium (plural: archegonia)

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The multicellular egg-producing organ in gametophytes and some vascular plants.

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Archenteron

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The principal cavity of a vertebrate embryo in the gestural stage; lined with endoderm, it opens up to the outside and represents the future digestive cavity.

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Arteriole

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A smaller artery, leading from the arteries to the capillaries.

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Artificial selection

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Change in the genetic structure of populations to the selective breeding by humans. Many domestic animal breeds and crop varieties have been produced through artificial selection.